Structure manufacturing method, structure manufacturing apparatus and intermediate structure
There is provided a structure manufacturing method, including: preparing an etching target with at least one surface comprising group III nitride; then in a state where the etching target is immersed in an etching solution containing peroxodisulfate ions; irradiating the surface of the etching target with light through the etching solution, and generating sulfate ion radicals from the peroxodisulfate ions and generating holes in the group III nitride, thereby etching the group III nitride, wherein in the etching of the group III nitride, the etching solution remains acidic during a period for etching the group III nitride by making the etching solution acidic at a start of etching the group III nitride, and the etching is performed, with a resist mask formed on the surface.
1. A structure manufacturing method, comprising:
preparing an etching target with at least one surface comprising group III nitride;
then in a state where the etching target is immersed in an etching solution containing peroxodisulfate ions;
irradiating the surface of the etching target with light through the etching solution, and generating sulfate ion radicals from the peroxodisulfate ions and generating holes in the group III nitride, thereby etching the group III nitride,
wherein in the etching of the group III nitride, the etching solution remains acidic during a period for etching the group III nitride by making the etching solution acidic at a start of etching the group III nitride, and
the etching is performed, with a resist mask formed on the surface.
2. The structure manufacturing method according to claim 1 , wherein a lowering range of pH of the etching solution at an end of the etching with respect to pH of the etching solution at a start of etching, is 4 or less.
3. The structure manufacturing method according to claim 1 , wherein a lowering range of the pH of the etching solution when all the peroxodisulfate ions contained in the etching solution are changed to sulfate ions, with respect to the pH of the etching solution at the start of etching, is 4 or less.
4. The structure manufacturing method according to claim 1 , wherein the etching solution contains a weak acid having an acid dissociation constant pK a of more than 0 and less than 7.
5. The structure manufacturing method according to claim 4 , wherein the weak acid is phosphoric acid.
6. The structure manufacturing method according to claim 4 , wherein a difference between the pH of the etching solution at the start of etching and the acid dissociation constant pK a of the weak acid is plus or minus 1 or less.
7. The structure manufacturing method according to claim 4 , wherein the pH of the etching solution at the start of etching is higher than the acid dissociation constant pK a of the weak acid.
8. The structure manufacturing method according to claim 4 , wherein the acid dissociation constant pK a of the weak acid is higher than the pH of the etching solution when all the peroxodisulfate ions contained in the etching solution are changed to sulfate ions.
9. The structure manufacturing method according to claim 1 , wherein the etching solution is not replaced during the period for etching the group III nitride.
10. The structure manufacturing method according to claim 1 , wherein the etching solution is not stirred during the period for etching the group III nitride.
11. The structure manufacturing method according to claim 1 , wherein the period for etching the group III nitride is 30 minutes or more.
12. The structure manufacturing method according to claim 1 , wherein the pH of the etching solution is measured during the period for etching the group III nitride.
13. The structure manufacturing method according to claim 12 , wherein a probe of a pH meter is placed at a position where a shadow of the probe due to the light is not reflected on the surface of the etching target, when measuring the pH of the etching solution.
14. The structure manufacturing method according to claim 1 , further comprising before the etching of the group III nitride:
lowering the pH of the etching solution by changing a part of the peroxodisulfate ions to sulfate ions by irradiating the etching solution with light in a state where the etching target is not immersed in the etching solution.
15. The structure manufacturing method according to claim 1 , wherein the sulfate ion radicals are generated by heating.
16. The structure manufacturing method according to claim 15 , wherein a wavelength of the light is 310 nm or more.
17. A structure manufacturing method, comprising:
preparing an etching target with at least one surface comprising group III nitride;
then in a state where the etching target is immersed in an etching solution containing peroxodisulfate ions;
irradiating the surface of the etching target with light through the etching solution, and generating sulfate ion radicals from the peroxodisulfate ions and generating holes in the group III nitride, thereby etching the group III nitride,
wherein in the etching of the group III nitride, the etching solution remains acidic during a period for etching the group III nitride by making the etching solution acidic at a start of etching the group III nitride, and
the etching is performed so that a root mean square surface roughness in a 5 μm square region of the surface etched by the irradiation of light is 2.76 nm or less.